This invention relates generally to apparatus and methods for processing workpieces, and more particularly to an apparatus and a method for manipulating and affixing tubular and nontubular workpieces.
Tubular materials constitute important components of a wide range of different devices. In application, it is often desirable or necessary to attach to a tubular material a second material or device which reinforces, strengthen, shapes, or otherwise improves the characteristics of the tubular material. Many techniques exist for performing work on tubular materials. These include, welding, molding, heat sealing and sewing.
Medical devices, are often made of a fabric or composite material which requires some form of reinforcement or other modification to improve its resistance to deformation or breakage. This is particularly the case for a useful class of medical devices, intraluminal stents, catheters and vascular prostheses.
Several types of therapeutic intraluminal devices are currently in clinical use, including catheters, vascular prosthesis and stents. In addition to those already in use, many new variations and improvements on these devices are being rapidly developed.
A stent, generally speaking, is a device that can be placed within the lumen, or interior space, of a tubular structure for supporting and assuring patency of a contracted, but otherwise intact, lumen. Patency, the state of being freely open, is particularly important in the field of angioplasty, which is concerned with the reconstruction of blood vessels. Stents are used, for example, for holding blood vessels open or for back tacking intimal flaps inside vessels after angioplasty. More generally, however, stents can be used inside the lumina of any physiological conduit including arteries, veins, vessels, the biliary tree, the urinary tract, the alimentary tract, the tracheobronchial tree, the genitourinary system, and the cerebral aqueduct. Furthermore, stents can be used inside lumina of animals other than humans.
In general, stents are prosthetic devices formed of a tubular body, the diameter of which can be decreased or increased. Stents are particularly useful for permanently widening a vessel that is either in a narrowed state, or internally supporting a vessel damaged by an aneurysm. Such stents are generally introduced to the body cavity by use of a catheter.
There are presently two classes of stents in widespread clinical use categorized with respect to their mode of expansion: balloon expandable and self expanding. Balloon expandable stents typically consist of slotted or wire mesh tubes that can be permanently expanded after operator controlled balloon inflation. See, for example, Palmaz: U.S. Pat. Nos. 4,739,762; 4,739,762; 4,776,337; and 5,102,417 and Strecker, E. P.; Liermann, D.; Barth, K. H.; Wolf, H. R. D.; Freudenberg, N.; Berg, G.; Westphal, M.; Tsikuras, P.; Savin, M.; and Schneider, B., Radiology, 175, 97-102 (1990).
Characteristically, self-expanding stents are loose wire meshes that can be compressed inside a sheath which, when removed, allows the stent to expand without the use of an inflating balloon. Many models are in common use including the MEDINVENT Registered TM stents, (See, Jedwab et al. J Appl. Biomatter 4: 77-85 (1993) and Gianturco et al., Amer. J. Radiology 151:673-676 (1988)). Further details regarding stents can be found in U.S. Pat. No. 3,868,956 (Alfidi et al.); U.S. Pat. No. 4,512,338 (Balko et al.); U.S. Pat. No. 4,553,545 (Maass et al.); U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882 (Gianturco); U.S. Pat. No. 4,856,516 (Hillstead); and U.S. Pat. No. 4,886,062 (Wiktor), which are incorporated herein in their entirety by reference thereto.
Useful intraluminal devices can be constructed from a variety of materials including fabrics, composites, metals, plastics and the like. Recent promising applications have relied on the use of shape-memory alloys. See, for example, U.S. Pat. No. 4,556,050 (Hodgson et al.), U.S. Pat. No. 4,485,816 (Krumme) and U.S. Pat. No. 5,597,378 (Jervis). In general, these devices take advantage of the alloy's transition temperature from marten site to austenite, to either dilate an incompetent blood vessel or hold segments of tissue together.
Shape-memory alloys possess the useful characteristic of being capable of changing physical dimensions upon heating above a first transition temperature between a soft martensitic metallurgical state and a hard austenitic metallurgical state of the alloys. A shape-memory alloy member can be processed while in a high temperature austenitic phase to take on a first configuration. After cooling the shape-memory alloy member below a second transition temperature between the austenitic and martensitic states without change of physical dimensions, the shape-memory alloy member can be mechanically deformed into a second configuration. The shape-memory alloy member will remain in this second configuration until further heating to a temperature above the first transition temperature at which time the shape-memory alloy member will revert to its first configuration.
A shape-memory alloy member can exert large forces on adjacent members during the transition from the second configuration to the first configuration. Numerous inventions have taken advantage of shape-memory alloy members capable of exerting this thermally activated force. Shape-memory alloys have the further useful characteristic that, in the martensitic phase, the stress-strain curve exhibits a plateau indicating that a limited increase in strain can be achieved with imperceptible increase in stress. This martensitic stress-strain plateau usually defines the range of mechanical strain which can be recovered by the application of heat. Exceeding the upper end of this strain range may result in non-heat recoverable deformation.
Another useful class of intraluminal devices includes various vascular prostheses. Since 1975, vascular prostheses composed of either knitted or woven Dacron.TM. fibers or expanded PTFE (Gore-Tex.TM.) have been established standards in anastomotic surgical arterial reconstruction. In the past decade, however, a steady growth of non-surgical transcatheter techniques and related devices have broadened both potential applications and overall suitability of endovascular reconstruction. In particular, angioplasty with or without endovascular stent placement has become an accepted adjunct in the management of atherosclerotic occlusive disease.
In the past, aneurysmal aortic disease has been treated almost exclusively by resection and surgical graft placement. In contrast to standard surgical repair, the use of an endovascular device does not entail the removal of the diseased aorta, but serves to create a conduit for blood flow in the event of subsequent aneurysm rupture. Endovascular aortic prostheses under current commercial development consist almost exclusively of grafts and stents attached together to form a single device. The stent secures the graft in a desired position and reduces the risk of late prosthetic migration.
In certain multicomponent embodiments of intraluminal devices, it is desirable to have attached to the device, one or more components which improve the operative characteristics of the device or expand its range of useful applications. For example, the intraluminal device can include struts or other supporting members attached thereto. Additionally, the device can also include one or more hinge-like members, rings, springs, collars, etc. Devices such as this are disclosed in U.S. Pat. No. 5,545,210 (Hess et al.)
Currently the assembly of multicomponent intraluminal devices based on a central tubular structure is hampered by the absence of machines which are capable of binding, by sewing or otherwise, components to a tubular device. Certain machines are known in the sewing art which are capable of stitching tubular materials.
For example, U.S. Pat. No. 4,530,294 (Pollmeier et al.) teaches an apparatus for holding tubular goods for stitching at the station of a sewing machine. The apparatus comprises a drum shaped support and the fabric is held to the drum by at least three arcuate segments which are radially displaceable and together from a segmented drum of a circumference wider than that of the inner drum. Similar to other devices currently found in the art, this device does not include ways of attaching additional elements onto a tubular intraluminal device.